A four-month-old baby was found to have teeth growing inside his brain.
The unnamed infant from Maryland, in the United States, had a rare type of brain tumour which contained a number of fully formed teeth.
The child underwent surgery to remove the growth, and is now making good progress, The New England Medical Journal reported.
Doctors first suspected something might be wrong when routine health checks showed the child’s head was growing at a faster-than-average rate.
An MRI scan revealed a tumour measuring 4.1cm by 4cm by 3.5cm and showed up structures on the right side of the mass which appeared similar to teeth in the lower jaw bone.
After the baby had undergone surgery, doctors identified the mass as a slow-growing tumour called adamantinomatous craniopharyngioma.
It is thought to have arisen from Rathke's pouch, an embryonic precursor to the pituitary gland.
These growths do not tend to spread outside the brain.
Dr. Narlin Beaty, a neurosurgeon at the University of Maryland Medical Center, who performed the boy's surgery along with his colleague, Dr. Edward Ahn, of Johns Hopkins Children's Center, told Live Science: "It's not every day you see teeth in any type of tumour in the brain. In a craniopharyngioma, it's unheard of."
He added that craniopharyngiomas commonly contain calcium deposits, "but when we pulled out a full tooth...I think that’s something slightly different".
It is now a year since the child underwent surgery and he is said to be progressing well.
However, he will have to undergo hormone treatments for the rest of his life.
Teeth have been found in people’s brains before, but only in tumours called teratoma, which have been reported to contain hair, teeth, bone and even eyes.